Summary: Schottky defect formation energy in MgO calculated by diffusion Monte Carlo
D. Alfè1,2
and M. J. Gillan2
1Department of Earth Sciences, University College London Gower Street, London WC1E 6BT, United Kingdom
2Department of Physics and Astronomy, University College London Gower Street, London WC1E 6BT, United Kingdom
Received 3 March 2005; published 13 June 2005
The energetics of point defects in oxide materials plays a major role in determining their high-temperature
properties, but experimental measurements are difficult, and calculations based on density functional theory
DFT are not necessarily reliable. We report quantum Monte Carlo calculations of the formation energy ES of
Schottky defects in MgO, which demonstrate the feasibility of using this approach to overcome the deficiencies
of DFT. In order to investigate system-size errors, we also report DFT calculations of ES on repeating cells of
up to 1000 atoms, which indicate that QMC calculations on systems of only 54 atoms should yield high
precision. The DFT calculations also provide the relaxed structures used in the variational and diffusion Monte
Carlo calculations. For MgO, we find ES to be in close agreement with results from DFT and from model
interaction potentials, and consistent with the scattered experimental values. The prospects for applying the
same approach to transition metal oxides such as FeO are indicated.
DOI: 10.1103/PhysRevB.71.220101 PACS number s : 61.72.Ji, 71.15. m
The quantum Monte Carlo QMC technique1,2 is impor-
tant in condensed matter science, because it is generally
much more accurate than density functional theory DFT